a review of desalination by solar still
Post on 23-Feb-2015
85 Views
Preview:
TRANSCRIPT
23-25 February 2006 NATO ARW Hammamet. Tunisia1
A Review of Desalinationby Solar Still
Hikmet S. AybarDepartment of Mechanical EngineeringEastern Mediterranean UniversityG.Magosa, KKTC, Mersin 10 Turkey
23-25 February 2006 NATO ARW Hammamet. Tunisia2
Introduction
Distillation is one of many processes available for obtaining fresh water from salty, brackish or contaminated water; and sunlight is one of several forms of heat energy that can be used to power that process. The aim of this study is to present basic principle of distillation by solar still, type of solar still systems, and the recent developments on the solar still systems.
23-25 February 2006 NATO ARW Hammamet. Tunisia3
Distillation by Solar Still
Solar still is a device to distillate impure water like brackish or saline water. It is a simple device to get potable/fresh distilled water from impure water, using solar energy as fuel.
23-25 February 2006 NATO ARW Hammamet. Tunisia4
Principle of Solar Still
23-25 February 2006 NATO ARW Hammamet. Tunisia5
Water Quality
In principle, the water from a solar still should be quite pure.The slow distillation process allows only pure water to evaporate from the pan and collect on the cover, leaving all particulate contaminants behind.
23-25 February 2006 NATO ARW Hammamet. Tunisia6
Types of Solar Still
The solar distillation systems are classified into two groups in term of energy supply:Passive Solar Stills: The passive solar still systems are conventional solar still systems which use solar energy as solely source of thermal energy.Active Solar Stills: In the active solar stills, an extra thermal energy is given to the passive solar still for faster evaporation.
23-25 February 2006 NATO ARW Hammamet. Tunisia7
Types of Solar Still
In terms of structure of the conventional solar still, different types of the basin-type solar still systems can be found in the literature:Single-slope double-basin solar still (Al-Karaghouliand Alnaser, 2004),Single-slop triple-basin solar still (El-Sebaii, 2005),Pyramid-shaped solar still (Fath et al. 2003b),Double-slope single-basin solar still (Al-Hayek and Badran, 2004).
23-25 February 2006 NATO ARW Hammamet. Tunisia8
Types of Solar Still
There are some other interesting solar still designs:Vertical Solar Still (Boukar and Harmin, 2005) which has vertical single-wick (holding the feed water) and vertical condensing surface.Vertical Solar Still with multiple vertical-wick and single vertical condensing surface with flat-plate reflector (Tanaka and Nakatake, 2005).
23-25 February 2006 NATO ARW Hammamet. Tunisia9
Types of Solar Still
Inclined Solar Distillation System (Aybar et al. 2005) in which water flows down on the inclined absorber plate (bare plate or covered with black wick) and evaporated water condenses on the inclined glass cover.Capillary Film Solar Still system (Bouchekimaet al., 2001).Basin-type Solar Still (El-Bahi and Inan, 1999) which is coupled with a condenser to increase the condensation rate.
23-25 February 2006 NATO ARW Hammamet. Tunisia10
Modeling of Solar Still
Any type of solar still systems can be modeled using energy balance and mass balance equations for the system.Since the main energy source is solar intensity which depends on the time during the day, the basic energy and mass balance equations must be time dependent.
23-25 February 2006 NATO ARW Hammamet. Tunisia11
Modeling of Solar Still
In the modeling of the solar still, the most important parameters are:Convection heat transfer coefficient to estimate heat transfer from the glass,Convection heat transfer coefficient to estimate heat losses from the bottom and sides of the cavity,Evaporation rate (or evaporation coefficient), andCondensation rate (or condensation coefficient).
23-25 February 2006 NATO ARW Hammamet. Tunisia12
Performance of Solar Still
The thermal instantaneous efficiency of a solar still is defined (Tiwari, 2002) as
The production rate performance (PRP) of absorber plate as (kg of distilled water per m2/ kJ solar energy per m2)
( ))()( tI
TThtI
q gwewewi
−==
&η
∑∑
∆⋅
∆⋅=
tItm
PRP i&
23-25 February 2006 NATO ARW Hammamet. Tunisia13
Conclusion
Solar still is most simple device to get potable/fresh distilled water from impure water using solar energy as fuel.Researchers have modified the conventional solar still system for better performance, such as multi-basin, multi-slop solar still systems, and coupled with solar collector to increase the water temperature.Especially, solar stills look like best choice to obtain fresh drinkable water in the remote areas for domestic usage.However, still the rate of distilled water production of the solar stills is low which is about 4-7 liters/day per meter square.
23-25 February 2006 NATO ARW Hammamet. Tunisia14
An Application:Inclined Solar Water Distillation System
Experimental and mathematical modeling studies have been performed on Inclined Solar Water Distillation System.Inclined Solar Water Distillation System generates fresh water and hot water at the same time.
23-25 February 2006 NATO ARW Hammamet. Tunisia15
System Description
23-25 February 2006 NATO ARW Hammamet. Tunisia16
Experimental Study
In the experimental study, three cases of the absorber plate have been tested:Bare absorber plate,Black-cloth wick,Black-fleece wick.
23-25 February 2006 NATO ARW Hammamet. Tunisia17
Results of Experimental Study
23-25 February 2006 NATO ARW Hammamet. Tunisia18
Results of Experimental Study
23-25 February 2006 NATO ARW Hammamet. Tunisia19
Description of Thermal Processes
23-25 February 2006 NATO ARW Hammamet. Tunisia20
Simulation Parameters
Parameter Symbol Value
Mass of absorber plate Mp (kg/m2) 7.9
Specific heat of absorber plate Cp (J/kg K) 477
Absorptivity of absorber plate α 0.96
Emissivity of absorber plate εp 0.08
Mass of glass Mg (kg/m2) 2.7
Specific heat of glass Cg (J/kg K) 800
Transmissivity of glass τ 0.88
Emissivity of glass εg 0.98
Density of water ρw (kg/m3) 989
Specific heat of water Cw (J/kg K) 4184
Mass of air Ma (kg) 0.24
Latent heat of vaporization hfg (J/kg) 2400×103
Convection heat transfer coefficient hc,p-w (W/m2 °C) 40
Convection heat transfer coefficient hc,g-a (W/m2 °C) 40
23-25 February 2006 NATO ARW Hammamet. Tunisia21
Changing of plate, water exit, and glass temperatures within time with constant solar intensity and constant air temperature.
0 1000 2000 3000 4000
Time (s)
25
35
45
55
65
T (°
C)
T PlateT WaterT Glass
23-25 February 2006 NATO ARW Hammamet. Tunisia22
Changing of evaporation and condensation rates, and relative humidity within time with constant solar intensity and constant air temperature.
0 1000 2000 3000 4000
Time (s)
0.00000
0.00002
0.00004
0.00006
0.00008
0.00010
0.00012
0.00014
0.00016
0.00018
Mas
s Fl
ow R
ate
(kg/
s)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Rel
ativ
e H
umid
ity
EvaporationCondensationRH
23-25 February 2006 NATO ARW Hammamet. Tunisia23
Changing of plate, water exit, and glass temperatures within time with variable solar intensity and air temperature.
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Time (hours)
20
30
40
50
60
70
80
90Te
mpe
ratu
re (°
C)
0
100
200
300
400
500
600
700
800
900
Sol
ar In
tens
ity (W
/m2 )
Solar IntT AirT PlateT WaterT Glass
12:00 Noon 5:00 PM
top related